Adult rat cardiomyocytes exhibit capacitative calcium entry

Abstract

Capacitative Ca2+entry (CCE) refers to the influx of Ca2+through plasma membrane channels activated on depletion of endoplasmic-sarcoplasmic reticulum Ca2+stores. We utilized two Ca2+-sensitive dyes (one monitoring cytoplasmic free Ca2+and the other free Ca2+within the sarcoplasmic reticulum) to determine whether adult rat ventricular myocytes exhibit CCE. Treatments with inhibitors of the sarcoplasmic endoplasmic reticulum Ca2+-ATPases were not efficient in releasing Ca2+from stores. However, when these inhibitors were coupled with either Ca2+ionophores or angiotensin II (an agonist generating inositol 1,4,5 trisphosphate), depletion of stores was observed. This depletion was accompanied by a significant influx of extracellular Ca2+characteristic of CCE. CCE was also observed when stores were depleted with caffeine. This influx of Ca2+was sensitive to four inhibitors of CCE (glucosamine, lanthanum, gadolinium, and SKF-96365) but not to inhibitors of L-type channels or the Na+/Ca2+exchanger. In the whole cell configuration, an inward current of ∼0.7 pA/pF at –90 mV was activated when a Ca2+chelator or inositol (1,4,5)-trisphosphate was included in the pipette or when Ca2+stores were depleted with a Ca2+-ATPase inhibitor and ionophore. The current was maximal at hyperpolarizing voltages and inwardly rectified. The channel was relatively permeant to Ca2+and Ba2+but only poorly to Mg2+or Mn2+. Taken together, these data support the existence of CCE in adult cardiomyocytes, a finding with likely implications to physiological responses to phospholipase C-generating agonists.